As a refrigeration or air conditioning hermetic compressor, there are conventional reciprocating type, rotary type and scroll type compressors, and these compressors are used in refrigeration or air conditioning fields of domestic or business purpose. Currently, compressors are developed while utilizing characteristics in terms of costs and performance.
Among them, a so-called hermetical compressor for preventing noise and eliminating the need of maintenance is a typical compressor in which a compressor mechanism and a motor are accommodated in a container, and a scroll compressor and a rotary compressor are in the mainstream. Generally, in the scroll compressor, a fixed scroll part in which a scroll lap rises from a mirror plate and an orbiting scroll part are meshed with each other to form a compression chamber therebetween, when the orbiting scroll part is allowed to orbit in a circular orbit while restraining the orbiting scroll part from rotating by a rotation-restraint mechanism, a compression chamber moves while changing its capacity, thereby carrying out the suction, compression and discharge, a predetermined back pressure is applied to an outer periphery of the orbiting scroll part and a back surface of a scroll lap by lubricant oil, so that the orbiting scroll part is not separated from the fixed scroll part and does not flip over.
According to the conventional scroll compressor, as shown in FIG. 4, a fixed scroll part 2 has a scroll lap 2a rising from a mirror plate 2b, and an orbiting scroll part 4 has a scroll lap 4a rising from a mirror plate 4b. The fixed scroll part 2 and the orbiting scroll part 4 are meshed with each other to form a compression chamber 5 therebetween. When the orbiting scroll part 4 is allowed to orbit in a circular orbit while restraining the orbiting scroll part 4 from rotating by a rotation-restraint mechanism 22, the compression chamber 5 moves while varying its capacity, thereby carrying out suction, compression and discharge.
That is, refrigerant gas sucked from a suction pipe 1 passes through a suction space 3 of the fixed scroll part 2 comprising the lap 2a and the mirror plate 2b, the refrigerant gas is enclosed in the compression chamber 5 formed by meshing the fixed scroll part 2 and the orbiting scroll part 4 comprising the lap 4a and the mirror plate 4b with each other, the refrigerant gas is compressed toward a center of the compression chamber 5 and is discharged from a discharge port 6.
A back pressure chamber 8 is formed such as to be surrounded by the fixed scroll part 2 and a bearing member 7. The back pressure chamber 8 always has back pressure for pushing the orbiting scroll part 4 against the fixed scroll part 2. A back pressure adjusting mechanism 9 is provided as means for always maintaining the back pressure at a constant level.
The back pressure adjusting mechanism 9 has a communication passage 10 which is in communication with the suction space 3 from the back pressure chamber 8 through the fixed scroll part 2. The communication passage 10 is provided with a valve 11. When the pressure in the back pressure chamber 8 becomes higher than a set pressure, the valve 11 is opened, lubricant oil in the back pressure chamber 8 is supplied to the suction space 3, and the pressure in the back pressure chamber 8 is maintained at a constant intermediate pressure.
On the other hand, lubricant oil accumulated in an oil reservoir 29 is introduced into an upper end of a shaft 13 through a passage 23 in the shaft 13 by an oil pump 31. The lubricant oil introduced into the upper end lubricates a sliding surface 33 and a sliding surface 34. A portion of the lubricant oil passes through a passage 24 in the orbiting scroll part 4, and is decompressed in a narrowed portion 12 and supplied to the back pressure chamber 8. The lubricant oil supplied to the suction space 3 is supplied to the compression chamber 5 together with the orbiting motion of the orbiting scroll part, and prevents refrigerant from leaking from the compression chamber 5, thereby enhancing the compression efficiency.
That is, the compression efficiency is enhanced by sealing using the lubricant oil. In a scroll compressor described in patent document 1 (Japanese Patent Application Laid-open No. 2000-110748), an involute winding end of the fixed scroll part is located directly above the discharge port, a suction port is formed in the vicinity of a suction passage so that the suction resistance of the scroll compressor is reduced, the suction efficiency is enhanced, and the compression efficiency is enhanced.
FIG. 5 is a diagram showing a relation between a supply rate of lubricant oil with respect to an amount of sucked refrigerant and a ratio of performance coefficient (ratio of COP) when R410A is used as the refrigerant and when carbon dioxide is used as the refrigerant. The diagram when the carbon dioxide was used was measured under the conditions of discharge pressure 9 MPa, suction pressure 5 MPa and rotation frequency 37 Hz. The diagram when R410A was used was measured using a scroll compressor which was designed such that refrigeration ability and frequency are substantially the same as those of the condition when the carbon dioxide was used. As can be found in FIG. 5, when R410A is used, as the supply rate of lubricant oil with respect to the amount of sucked refrigerant is smaller, the ratio of performance coefficient is more enhanced.
However, it is difficult to appropriately supply lubricant oil to the suction space only by reducing the suction resistance as in the scroll compressor described in patent document 1, and the compression efficiency is adversely influenced and its performance is deteriorated.
That is, lubricant oil supplied to the suction space is swept away along the flow of the refrigerant and more lubricant oil is supplied to a compression chamber formed in a center direction of the orbiting scroll part. Therefore, lubricant oil supplied to the compression chamber formed in the outer peripheral direction of the orbiting scroll part becomes insufficient, the leakage in the outer peripheral side compression chamber is increased, and the performance is deteriorated. If the supply rate of lubricant oil is increased to compensate the oil supply shortage in the outer peripheral direction of the orbiting scroll part, suction overheat is caused and the volumetric efficiency is deteriorated.
A flow path of the refrigerant entering the suction space is largely bent until the refrigerant is enclosed in the compression chamber. At that time, there is a problem that the refrigerant collides against a wall surface or a swirl is formed, pressure loss is generated and the performance is deteriorated.
As a control method for reducing the supply rate of lubricant oil to enhance the performance coefficient, there are a method for increasing pressure loss of the narrowed portion 12, and a method for increasing the set pressure in the back pressure chamber 8 to make it difficult to open the valve 11. In the case of the former method, if the narrowed portion 12 is reduced, the possibility that the narrowed portion 12 is closed by contamination is increased, and when the narrowed portion 12 is closed, the lubricant oil is not supplied to the compression chamber 5, galling or abnormal wearing is generated, and the reliability of the compressor is largely deteriorated. In the case of the latter method, if the set pressure is increased, a force for pushing the orbiting scroll part 4 against the fixed scroll part 2 is abnormally increased at the time of high load operation. As a result, galling or abnormal wearing is generated in the pushing surface, and the reliability of the compressor is largely deteriorated. The methods for controlling the supply rate of lubricant oil have such problems.
Further, if HFC-based refrigerant or HCFC-based refrigerant is used as the refrigerant, since the refrigeration effect per unit circulation amount is small as compared with carbon dioxide, the lap 4a of the orbiting scroll part 4 is increased in height. Thus, there is a problem that pressure loss is generated by swirl generated during the suction process, the suction efficiency is deteriorated, and since the refrigerant and lubricant oil are not sufficiently, leakage loss is increased.
When carbon dioxide is used as the refrigerant, as can be found in FIG. 5, an optimal value at which the ratio of performance coefficient becomes maximum exists in the supply rate of lubricant oil with respect to the amount of sucked refrigerant. However, since a pressure difference between discharge pressure and suction pressure is about 7 to 10 times higher than that of the conventional refrigeration cycle using CFCs as the refrigerant, small shortage of seal oil increases leakage of compression chamber, and the performance is deteriorated.
The present invention has been accomplished in view of the conventional problems, and it is an object of the invention to provide a simple, inexpensive, efficient and reliable scroll compressor.